物理 1983 年 DSE、CE 選擇題（第 2 頁）

11.

When $40$ kg of water falls through a certain distance, its temperature is increased by $0.2^\circ\mathrm{C}$ . What is the height through which it has fallen ? Given : Specific heat capacity of water $= 4200\ \mathrm{J\,kg^{-1}\,{}^\circ C^{-1}}$

12.

It is given that : the specific latent heat of fusion of ice $= 3.3\times10^5\ \mathrm{J\,kg^{-1}}$ the specific latent heat of vaporization of water $= 2.3\times10^6\ \mathrm{J\,kg^{-1}}$ If $1$ kg of ice at $0^\circ\mathrm{C}$ and $1$ kg of steam at $100^\circ\mathrm{C}$ are mixed in a well insulated vessel, the result will be

13.

$Ray PQR in a semi-circular glass slab with Q at the centre, and possible directions W, X, Y and Z of the refracted ray$

In the diagram, $PQR$ represents the path of a ray of light incident on a semi-circular glass slab. $Q$ is the centre of the slab. Which of the directions $W$ , $X$ , $Y$ or $Z$ correctly indicates the subsequent path of the refracted ray ?

14.

Lamp, lens and screen with the sharp image formed at P in front of the screen

A lens gives a sharp image of the lamp at $P$ as shown in the figure above. Which of the following methods could give a sharp image of the filament on the screen ?

(1)Move the screen towards the lens.

(2)Move the lamp closer to the lens.

(3)Replacing the lens by another lens of longer focal length.

15.

Which of the following statements about the properties of light is/are correct ?

(1)The speed of light in vacuum is independent of its wavelength.

(2)The wavelength of light will change when it enters a less dense medium.

(3)The frequency of light will change when it enters a less dense medium.

16.

Which of the following statements concerning the properties of virtual images formed by a lens is/are correct ?

(1)Virtual images can be seen by the naked eye.

(2)Virtual images can be formed on a screen.

(3)Virtual images can be photographed with a camera.

17.

An object is placed $20$ cm in front of a converging lens of focal length $30$ cm. Which of the following statements about its image is/are correct ?

(1)The image is real.

(2)The image is magnified.

(3)The image is erect.

18.

Given that the approximate wavelength of red light is $7\times10^{-7}$ m, what is the approximate wavelength of an FM radio wave ?

19.

An ultrasonic wave is sent from a ship to find the depth of the sea-bed. A signal is received $0.2$ s later. Given that the speed of sound in sea water is $1500\ \mathrm{m\,s^{-1}}$ , what is the depth of the sea-bed ?

20.

A stationary wave is set up along a string by a vibrator as shown in the diagram. If the frequency of the vibrator is $5$ Hz, what is the velocity of the wave set up in the string ?

Stationary wave on a string with four loops spanning 20 cm